Expectation for a fuel cell has been elevated as a power supply for a portable electronic device used in information society in recent years or as a power supply for coping with air pollution or global warming. Among the fuel cells, a direct methanol type fuel cell (hereinafter, referred to as DMFC: Direct Methanol Fuel Cell) in which power generation is performed by directly taking out protons from methanol provides characteristics that a reformer is not required and the volume energy density is high and thus application to a portable electronic device has been increasingly expected.
Various DMFC's have been proposed which are provided with a power generating device having a power generating part (cell), an accommodating vessel for accommodating methanol or methanol aqueous solution (hereinafter, referred to as methanol), and a liquid feed pump for feeding methanol forcibly from the accommodating vessel (see, for example, Japanese Patent Laid-Open No. 2004-71262, Japanese Patent Laid-Open No. 2004-127618, and Japanese Patent Laid-Open No. 2004-152741).
The cell includes an anode electrode (fuel electrode) having an anode collector and an anode catalyst layer, a cathode electrode (air electrode) having a cathode collector and a cathode catalyst layer, and an electrolyte membrane disposed between the anode electrode and the cathode electrode. Methanol is supplied to the anode electrode by a liquid feed pump and air is supplied to the cathode electrode by an air supply pump.
The activity of methanol oxidation is low in the anode electrode of the cell which is the power generating part of an above-mentioned DMFC and thus a voltage loss occurs. Further, a voltage loss occurs in the cathode electrode. Therefore, an output capable of being obtained from one cell becomes extremely low. Accordingly, a plurality of cells is used in the DMFC to obtain a prescribed output.
When methanol is excessively supplied to the anode electrode, a so-called crossover occurs which means that a part of the methanol transmits through the electrolyte membrane in an unreacted state and leaks to the cathode electrode. Since the crossover causes the electric potential of the cathode electrode to decrease, the voltage loss occurs in the cathode electrode. Further, unreacted methanol that reaches the cathode electrode is not related to power generation but reacts with oxygen to generate heat, and thus the power-generating efficiency in the cell is significantly reduced by the crossover. Accordingly, it is preferable not to supply excessive methanol to the anode electrode.
As described above, as a liquid feed pump for supplying methanol to the anode electrode of a cell, it has been desired which is provided with characteristics that discharge to a plurality of cells is possible and an appropriate amount of methanol can be accurately discharged. However, the liquid feed pump having such characteristics has not been proposed.